main() {
    *(char *)0x2000 = 'a';  //内存2000:0000写入'a'
    *(int *)0x2000 = 0xf;   //2个字节写入000f
    *(char far *)0x20001000 = 'a';//2000:1000 写入‘a’

    _AX = 0x2000;
    *(char *)_AX = 'b';

    _BX = 0x1000;
    *(char *)(_BX + _BX) = 'a';
    *(char far *)(0x20001000 + _BX) = *(char *)_AX //2000:3000 写入 'a'
}
